In a timepiece for digitally displaying time information and calendar information, or in a combination timepiece made by combining the digital display of them and an analog display using hands, a liquid crystal display panel is used to perform the digital display.
In such a conventional timepiece using the liquid crystal display panel, a battery of simple consumption-type or charging-type is typically used as an energy source (electric power source), and additionally there is one type in which a solar battery is provided around the liquid crystal display panel, and electric power generated by it is accumulated in a secondary battery to use.
When the earth's environmental problems and energy problems are focused on, the simple consumption-type battery will have a serious problem in waste-disposal in the future, or the charging-type battery will have an energy consumption problem if it is charged through supply of electric power from an external power source.
Further, replacement of batteries is not preferable, especially for a timepiece, in maintaining a good waterproof state and in the prevention of the introduction of dust into its case. Further, a timepiece has low power consumption, and thus its timepiece system can be driven with little quantity of power generation. Therefore, it is preferable to install a solar battery in the timepiece to supply the entire or at least a part of the consumed electric power by power generation of the solar battery, thereby offering a great expectation of no waste produced and self-sufficient energy in the future.
In the timepiece using the conventional solar battery as the energy source, however, the solar battery is too conspicuous, and additionally it is necessary to secure a relatively large area for the solar battery, causing great restriction in visual design.
An example of a timepiece using a conventional solar battery as an energy source is explained here with reference to the drawings.
FIG. 35 is a schematic plan view showing an example of a conventional digital wristwatch with solar batteries. FIG. 36 is a schematic cross-sectional view taken along a line XXXVI—XXXVI in FIG. 35.
In this wristwatch, as shown in FIG. 35, a liquid crystal display panel 9 is disposed at the center of the upper surface of a watch case 1, and a number of solar batteries 15 are arranged in rows on both sides of the liquid crystal display panel 9.
The liquid crystal display panel 9 is provided with a chronograph display portion 3, a year-month-date display portion 4 and a time display portion 5. Further, four mode adjusting buttons 10 for correcting display contents, adjusting time and the like are provided on the side face of the watch case 1.
The watch case 1 seals the inner space with a cover glass 2 and a case back 7 as shown in FIG. 36.
In the watch case 1, the liquid crystal display panel 9 and fours solar batteries 15 provided on either side thereof are arranged inside the cover glass 2. A circuit board 6 is disposed below them, which includes a timepiece circuit operating by being supplied with electric power from the solar batteries 15, a drive circuit for driving the liquid crystal display panel 9, and the like.
Around the solar batteries 15 and the liquid crystal display panel 9, a panel cover 25 is provided, which shields electrodes and their outer forms.
In the liquid crystal display panel 9, a first substrate 21 and a second substrate 22, each of which is made of transparent glass or the like, are bonded together opposed each other with a predetermined gap interposed therebetween with spacers (not shown) and a sealing portion 23, and a liquid crystal layer 14 is sealed in the gap.
The opposed inner faces of the first substrate 21 and the second substrate 22 are provided with signal electrodes, opposed electrodes opposed to the signal electrodes to form pixel portions, and alignment films, though their illustration is omitted. A twisted nematic (TN) liquid crystal with a twist angle of 90 degrees is used for the liquid crystal layer 14.
In order to allow a change in alignment state of liquid crystal molecules caused by voltage applied to the liquid crystal layer 14 used in the liquid crystal display panel 9 to be viewed, a first polarizing film 16 and a second polarizing film 17 are bonded to the upper side of the first substrate 21 and the lower side of the second substrate 22 respectively with an acrylic resin. Each of the first and second polarizing films is an absorption-type polarizing film of which one polarizing optical axis is a transmission axis and a polarizing optical axis perpendicular thereto is an absorption axis, and the first polarizing film 16 and the second polarizing film 17 are arranged so that the respective transmission axes are perpendicular to each other.
This brings a portion where voltage is not applied between the signal electrode and the opposed electrode of the liquid crystal display panel 9 into a light transmission state, and a portion where voltage is applied into a light absorption state, thereby presenting a display.
Further, a translucent-type reflector 18 made by evaporating aluminum (Al) film to a transparent resin film is bonded to the lower side of the second polarizing film 17, and, opposed to that, an auxiliary light source 19 composed of an electro-luminescent (EL) element is provided on the circuit board 6.
When an external light source is dark, that is, when the environment of the watch in use is dark, the auxiliary light source 19 is turned on. Emitted light from the auxiliary light source 19 is made incident on the liquid crystal display panel 9 through use of transmission characteristics of the translucent-type reflector 18, presenting a transmission-type display.
When the external light source is bright, use of reflection characteristics of the translucent-type reflector 18 enables a reflection-type display.
A secondary battery 8 for accumulating electric power generated by the solar batteries 15 is provided on the back face side of the circuit board 6. These constituted a timepiece module having a function of generating electric power.
There also is a combination watch though the illustration thereof is omitted, which digitally displays lap time of a chronograph and a year, a month and a date by a liquid crystal display panel and includes an hour hand, a minute hand and further a second hand to analog-display time with the hands, in which solar batteries are annularly arranged at the peripheral portion of a dial, and electric power generated by the solar batteries is used as electric power for a liquid crystal display and drive of the hands.
In either structure of the conventional timepieces (watches), the solar batteries are viewed from the outside, which is not preferable in visual design. The liquid crystal display panel and the solar battery are located at different positions, making an outer form of the timepiece large as compared to the proportion of the display area of the liquid crystal display panel. Further, there also is a problem that a large display area of the liquid crystal display panel occupies a space where the solar battery is disposed.